Re: [FFmpeg-devel] [PATCH 2/2] Don't use CMOV in MMX code
On Fri, 2014-09-12 at 14:53 -0700, Daniel Kang wrote: > > > > >All processors supporing mmx2 also support cmov, so if a test for > > mmx2 > succeeds, we can use cmov. > > Since I originally thought mmx => cmov (and apparently am wrong) is > there > official documentation supporting this? > As an example, here's the /proc/cpuinfo contents for my AMD K6 box. You'll note that on the flags line it does have 'mmx', but does not have 'cmov'. (It also doesn't have 3dnow; that was introduced in later chips in the K6 series.) I'm actually looking into getting FATE running on this box right now, we'll see how that goes. processor : 0 vendor_id : AuthenticAMD cpu family : 5 model : 7 model name : AMD-K6tm w/ multimedia extensions stepping: 0 cpu MHz : 266.603 cache size : 64 KB fdiv_bug: no f00f_bug: no coma_bug: no fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr cx8 mmx bogomips: 533.42 clflush size: 32 cache_alignment : 32 address sizes : 32 bits physical, 32 bits virtual power management: -- Calvin Walton ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH 2/2] Don't use CMOV in MMX code
On Fri, 12 Sep 2014, Daniel Kang wrote: > > All processors supporing mmx2 also support cmov, so if a test for mmx2 > > succeeds, we can use cmov. > Since I originally thought mmx => cmov (and apparently am wrong) is there > official documentation supporting this? There is no official documentation, it is just a historical fact. MMX2 was introduced in Pentium 3 (it already has CMOV) and in Athlon (it also has CMOV). Mikulas___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH 2/2] Don't use CMOV in MMX code
On Fri, Sep 12, 2014 at 11:53 PM, Daniel Kang
wrote:
>>All processors supporing mmx2 also support cmov, so if a test for mmx2
> succeeds, we can use cmov.
>
> Since I originally thought mmx => cmov (and apparently am wrong) is there
> official documentation supporting this?
CMOV was introduced in the P6 architecture, which is Pentium Pro, or i686.
MMX came before in P5 already ("Pentium with MMX Technology")
Its probably in Intel's Software Developer’s Manual somewhere, but I
couldn't find it on a moments notice, only the instruction sets like
MMX/SSE/... are listed very prominently.
- Hendrik
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Re: [FFmpeg-devel] [PATCH 2/2] Don't use CMOV in MMX code
>All processors supporing mmx2 also support cmov, so if a test for mmx2 succeeds, we can use cmov. Since I originally thought mmx => cmov (and apparently am wrong) is there official documentation supporting this? ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH 2/2] Don't use CMOV in MMX code
On 12/09/14 4:50 PM, Mikulas Patocka wrote: > There are MMX processors that don't support CMOV (pentium-mmx, amd-k6, cyrix > 6x86). Therefore, we must not use cmov in in MMX code. > > All processors supporing mmx2 also support cmov, so if a test for mmx2 > succeeds, > we can use cmov. > > --- > libavcodec/x86/h264_idct.asm |6 ++ > 1 file changed, 6 insertions(+) > > Index: ffmpeg/libavcodec/x86/h264_idct.asm > === > --- ffmpeg.orig/libavcodec/x86/h264_idct.asm 2014-08-25 03:59:06.376569389 > +0200 > +++ ffmpeg/libavcodec/x86/h264_idct.asm 2014-08-25 18:47:46.988574579 > +0200 > @@ -1063,7 +1063,13 @@ cglobal h264_luma_dc_dequant_idct, 3, 4, > addt3d, 128 << 16 > movt1d, 7 > cmpt0d, t1d > +%if cpuflag(mmx2) > cmovg t0d, t1d > +%else > +jng .skip_mov > +movt0d, t1d > +.skip_mov: > +%endif > inct1d > shrt3d, t0b > subt1d, t0d This is not necessary. The check for cmov-enabled CPUs is done in h264dsp_init.c so this function is not being used on CPUs like the ones you mentioned. If anything, you could add a second mmx version for said CPUs, but i really doubt it's worth the increased binary size. ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
[FFmpeg-devel] [PATCH 2/2] Don't use CMOV in MMX code
There are MMX processors that don't support CMOV (pentium-mmx, amd-k6, cyrix 6x86). Therefore, we must not use cmov in in MMX code. All processors supporing mmx2 also support cmov, so if a test for mmx2 succeeds, we can use cmov. --- libavcodec/x86/h264_idct.asm |6 ++ 1 file changed, 6 insertions(+) Index: ffmpeg/libavcodec/x86/h264_idct.asm === --- ffmpeg.orig/libavcodec/x86/h264_idct.asm2014-08-25 03:59:06.376569389 +0200 +++ ffmpeg/libavcodec/x86/h264_idct.asm 2014-08-25 18:47:46.988574579 +0200 @@ -1063,7 +1063,13 @@ cglobal h264_luma_dc_dequant_idct, 3, 4, addt3d, 128 << 16 movt1d, 7 cmpt0d, t1d +%if cpuflag(mmx2) cmovg t0d, t1d +%else +jng.skip_mov +movt0d, t1d +.skip_mov: +%endif inct1d shrt3d, t0b subt1d, t0d ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
